tcmalloc: Use the default TLS model on arm-gcc, CrOS only.

third_party/tcmalloc/chromium/src/thread_cache.cc

 // Copyright (c) 2008, Google Inc.
 // All rights reserved.
 //
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 // notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
@@ skipping 48 matching lines @@
 size_t ThreadCache::overall_thread_cache_size_ = kDefaultOverallThreadCacheSize;
 ssize_t ThreadCache::unclaimed_cache_space_ = kDefaultOverallThreadCacheSize;
 PageHeapAllocator<ThreadCache> threadcache_allocator;
 ThreadCache* ThreadCache::thread_heaps_ = NULL;
 int ThreadCache::thread_heap_count_ = 0;
 ThreadCache* ThreadCache::next_memory_steal_ = NULL;
 #ifdef HAVE_TLS
 __thread ThreadCache* ThreadCache::threadlocal_heap_
 // See comments in thread_cache.h about this. Bug here:
 // http://code.google.com/p/chromium/issues/detail?id=124489
-#if defined(HAVE___ATTRIBUTE__) && !defined(PGO_GENERATE)
+//
+// gcc has a problem with this tls model on arm.
+// See https://bugs.chromium.org/p/chromium/issues/detail?id=650137
+#if defined(HAVE___ATTRIBUTE__) && !defined(PGO_GENERATE) && \
+    (defined(__clang__) || !defined(OS_CHROMEOS) || !defined(__arm__))

[llozano, 2017/01/19 21:38:42]

not gcc does not necessarily mean clang. Is it?

I prefer to read this condition like 
!(GCC && OS_CHROMEOS && ARM)

[llozano, 2017/01/19 22:11:03]

ah, but on ChromeOS .. not GCC implies clang..

[laszio, 2017/01/19 22:11:46]

Done.

    __attribute__ ((tls_model ("initial-exec")))
 # endif
    ;
 #endif
 bool ThreadCache::tsd_inited_ = false;
 pthread_key_t ThreadCache::heap_key_;
 
 #if defined(HAVE_TLS)
 bool kernel_supports_tls = false;      // be conservative
 # if defined(_WIN32)    // windows has supported TLS since winnt, I think.
@@ skipping 425 matching lines @@
 void ThreadCache::set_overall_thread_cache_size(size_t new_size) {
   // Clip the value to a reasonable range
   if (new_size < kMinThreadCacheSize) new_size = kMinThreadCacheSize;
   if (new_size > (1<<30)) new_size = (1<<30);     // Limit to 1GB
   overall_thread_cache_size_ = new_size;
 
   RecomputePerThreadCacheSize();
 }
 
 }  // namespace tcmalloc